The invention generally relates to the field of oilfield exploration, production, and testing, and more specifically, to the use of materials designed to create debris-free perforating apparatus and techniques for enhanced hydrocarbon recovery.
For purposes of enhancing fluid communication between wellbore and geological rock formation containing hydrocarbons, holes are punched from the wellbore to the rock formation during operations, known in the oilfields as perforating operations. More specifically, during these operations a long and tubular device called a perforating gun is run into the wellbore in preparation for production. After the perforating gun has been deployed at its appropriate position downhole, perforating charges (shaped charges, for example) contained within the perforating gun are fired. As a result of firing these shaped charges, extremely high-pressure jets capable of opening perforation tunnels through both casing and liner (if the wellbore is cased) are produced, and a skin of the surrounding rock formation is then made more permeable for releasing its hydrocarbons.
The shaped charges are designed so that a cavity-effect explosive reaction is produced and focused in a high-pressure and high-velocity jet that can force materials, such as steel (casing), cement and rock formations, to fracture and then flow plastically around the jet and effectively open a perforation tunnel. Shaped charges may be classified according to the tunnel depth their perforation jet forms and the tunnel cross-sectional diameter (called the “hole size”) at its entrance. One type of shaped charge, referred as a “big hole” shaped charge, produces a relatively large-diameter hole in the casing and has a relatively shallow penetration depth into the rock formation. Such “big hole” shaped charges are commonly employed in sand control applications. Another type of popular shaped charge is a “deep penetrating charge.” Such a shaped charge leaves a relatively smaller-diameter hole in the well casing but has the advantage of penetrating relatively farther into the geological rock formation. The greater penetration depth associated to these charges is hugely beneficial to extend well fluid communication past any damage zone (caused by drilling of the wellbore), and it also tends to significantly enhance well productivity. Deep penetrating charges are employed in natural completion applications.
The shaped charges may be contained either inside a tubular member as part of a hollow carrier perforating gun or may be individually encapsulated. In order to prevent deteriorating the explosives contained within the shaped charges due to inadvertent contact with well fluids, each shaped charge is sealed by a corresponding cap. By being more massive, the encapsulated shaped charges tends to produce significantly more debris than the same size charges that are carried by a hollow carrier perforating gun. The encapsulated charges also tend to generate larger diameter holes in the casing that extend deeper into the geological rock formation.
The firing of the perforating gun results in debris from both the shaped charges and other parts of the gun located in close proximity to the explosives. Though the debris is largely contained within the perforating gun and the wellbore, some debris is inescapably introduced into the rock formation. In situations where significant debris (in particular from the shaped charge liner) reaches the rock formation, the productivity of the well may be hindered, resulting in a problem often referred as “skin damage”. To mitigate the detrimental consequences of debris left in the perforating tunnel, perforating is generally conducted underbalanced (i.e., in conditions wherein the wellbore possesses a lower pressure than the formation pressure) since a higher formation pressure causes debris to evacuate with the formation fluids surged into the well. Today, other methods of stimulation such as acidizing and propellent fracturing are often used for purposes of overcoming this damage and bringing the well up to its full potential. If not property conducted, perforating debris may induce significant losses with regard to time and cost operating the well. As example, an extra intervention may be needed in the well to remove debris from a fractured zone. Of considerable concern to a field operator, the debris may cause additional damage to the well, such as damage caused to a packer elastomer seal or damage due to the clogging of a downhole choke, for example.
Thus, there is a continuing need for new and/or improved solutions to minimize the amount of debris in a well and therefore, offer new and improved perforating operations.